An Active-Matrix Organic Light Emitting Diode (AMOLED) display apparatus is a self-luminous element based on Organic Light Emitting Diodes (OLEDs). The light emitting principle of each OLED is that an organic semiconductor material and a light emitting material are subjected to carrier injection and compounding under the drive of an electric field so as to emit light. Due to various advantages of high brightness, high image quality, ultra small thickness, good display efficiency and the like, the AMOLED display apparatus is hopeful to be more widely applied.
The AMOLED display apparatus consists of thousands of pixels, and each pixel includes an OLED and a pixel circuit for driving the OLED. Each pixel circuit consists of a switching Thin-Film Transistor (TFT), a capacitor and a drive TFT. Each switching TFT charges a voltage corresponding to a data signal to the corresponding capacitor, the corresponding drive TFT regulates a current supplied to the corresponding OLED according to the voltage of the capacitor, and a luminous quantity of the OLED is in direct proportion to the current, so that brightness of the OLED is regulated.
However, due to imperfect process and the like, the drive TFTs of all the pixels have specific differences in threshold voltage Vth, and migration rate so as to cause different currents of all the pixels, which are used for driving the OLEDs, and brightness distortions among all the pixels. A visual result is that the original specific differences of the drive TFTs cause spots or patterns on a screen, and in the subsequent driving process, the drive TFTs can reduce the service life of an AMOLED display panel or generate image retention due to the specific differences generated by degradation.
In order to solve this problem, the Chinese Patent CN102968954A discloses an AMOLED display apparatus capable of rapidly sensing a current of each pixel so as to compensate the brightness distortions among the pixels, and a method for sensing the current of each pixel of the AMOLED display apparatus. According to this patent, parasitic capacitors (i.e., line capacitors) on column-oriented lines (e.g., datum lines, data lines or first power lines and the like) on a display screen are utilized, the parasitic capacitors are charged by currents of the drive TFTs, voltages obtained after charging are input into an Analog-to-Digital Converter (ADC) module, and then the currents of the pixels are calculated by utilizing a formula I=Cx(V2−V1)/(t2−t1).
However, due to limitations of process, e.g., an uneven film-forming thickness and the like, the capacitors of all the column-oriented lines on the display screen may be different, and moreover, the ADC module in an integrated circuit has an error for conversion of each channel, both of which can influence sensing of the currents so as to cause inaccurate compensation on the brightness distortions of the pixels.